Tree Peony Care Through the Year: Watering, Feeding and Supporting the Flowers

Water deeply and rarely, and never let it sit wet

A tree peony puts down a deep, fleshy root system and draws on moisture well below the surface. Once established, it needs watering only in genuine drought, and then thoroughly: 3 to 4 gal (12 to 15 liters) poured slowly at the base so the water reaches 12 in (30 cm) down, rather than a daily sprinkle that only wets the mulch. Two good soakings a month through a dry summer beat daily light watering every time.

The danger is always the other way. Ground that stays saturated after rain rots the roots and, on a young grafted plant, rots the buried stem before it has rooted for itself. If the soil around the base is dark and greasy a day after rain, and the leaves are yellowing from the bottom of the plant upward while the soil is plainly wet, the problem is drainage rather than drought. Stop watering, pull the mulch back from the base to let the surface dry, and plan to raise the bed.

Water at the base, never over the leaves. Wet foliage overnight is exactly the condition botrytis needs, and a tree peony that is regularly sprinkled from above will get gray mold in the buds. In a container, which is much less forgiving, water when the top 2 in (5 cm) of compost has dried and always let the pot drain fully; never leave it standing in a saucer of water.

The first two summers after planting are the exception. A newly planted tree peony has not yet reached deep moisture, so water it every week or ten days through its first two dry seasons even when an established plant nearby needs nothing.

Feed lightly, twice, and stop by midsummer

Tree peonies flower on wood and store the energy for it slowly. They do not want the heavy nitrogen feeding that pushes leafy growth, which produces soft shoots that flop, attract botrytis and fail to ripen before frost. Two light feeds a year is the whole program.

The first goes on as the buds begin to swell and the red new shoots push, using a balanced granular feed or one slightly higher in potassium, scattered over the root area at the rate on the pack and scratched into the surface. The second goes on straight after flowering finishes, when the plant is building next year's buds; this one matters more than most gardeners realize, because the flowers you see next spring are being made in the weeks after this one. Stop all feeding by midsummer so the new wood hardens before cold weather.

Top the mulch up once a year in autumn with 2 in (5 cm) of well rotted compost or leaf mold over the root area, keeping it clear of the stems. On thin or strongly acidic soil, a scattering of garden lime every second or third year keeps the pH in the neutral range these plants prefer. Do not dig or fork around an established plant; the surface roots run wide and cutting them costs flowers.

Wind, sun and support for flowers that outweigh their shoots

The flowers are the largest of any hardy shrub, up to 8 in (20 cm) across, and they are carried on the current season's soft new growth. A heavy double bloom that catches rain weighs enough to bend its shoot to the ground and sometimes to snap it at the join with the old wood. Losing a shoot that way costs you the wood as well as the flower.

Put support in before the buds fatten, not after they have flopped. Three or four canes with soft ties, or a purpose made ring set at about two thirds of the plant's height, are enough. Tie loosely, around the shoot rather than tight against it, and check the ties once a season as the wood thickens; a forgotten tight tie will girdle a stem in two years.

The site does most of the work. A tree peony wants half a day of sun and shelter from the prevailing wind, with shade during the hottest hours of the afternoon. In blazing all day sun the flowers bleach and last two days rather than a week, and in deep shade the plant grows leggy and flowers thinly. An east facing spot with a wall or hedge to the windward side, and morning sun that dries the foliage early, suits it almost perfectly.

1. Check ties and supports as the shoots extend Once new growth is 6 in (15 cm) long, set canes or a ring. Doing it after the buds are heavy means working around brittle shoots that snap when you move them.
2. Clear the crown of last year's debris Rake fallen leaves and any old flower remains out from the base before growth starts. Debris held against the stems is where botrytis spores overwinter.
3. Feed at bud swell Scatter a balanced granular feed over the root area, scratch it into the surface and water it in if the soil is dry. Keep it off the stems and leaves.
4. Shade the open flowers if you want them to last A temporary screen or a parasol over the plant during flowering in hot, bright weather can double the life of the blooms. This is optional, not necessary.
5. Feed again straight after flowering Next spring's buds are set within about eight weeks of the last flower fading. A second light feed and steady moisture in that window is what fills them.

Plants in containers, and plants that look tired

A tree peony will live in a large container, but it needs a big one: at least 18 to 24 in (45 to 60 cm) across and as deep, in a soil based compost rather than a peat free multipurpose that collapses in two years. The graft union still needs to be buried 4 to 6 in (10 to 15 cm) deep, which means starting with the pot only part filled. Container plants dry out faster, freeze harder at the root, and need repotting or top dressing every three or four years in autumn.

A plant that looks tired but has no visible disease is almost always telling you about its roots. Yellow leaves with wet soil means drainage. Few, short new shoots with pale foliage across the whole plant means starvation or competition from a neighboring shrub's roots. Sudden collapse of one branch while the rest looks fine is usually botrytis or physical damage at the base of that branch, not a whole plant problem.

Resist the urge to intervene hard. Tree peonies respond slowly to everything, good and bad. Correct the drainage, the feeding or the shade, then wait a full season before deciding whether it worked. Repeatedly digging around a slow plant is the most reliable way to kill it.

The notes that make next year easier

Record how much you watered and when, in a dry summer. Tree peonies show drought stress late and recover slowly, and a written record of the gap between soakings is the only way to learn what your particular soil can carry. Note the day the leaves first looked dull or the edges browned; that is your plant's threshold.

Write down the dates of both feeds and what you used. Because the second feed pays off nine months later, in flowers, you cannot judge it from memory. Two or three years of paired records, feed date against the following spring's bud count, tell you far more than any general recommendation.

Note which shoots needed support, and where they bent. Heavy shoots tend to be the same ones each year, on the same side of the plant, usually the side reaching for the light. Knowing which side flops lets you set two canes in the right place rather than caging the whole shrub.